1. Field of the Invention
The present invention concerns an exposure apparatus used in photolithography processes in the manufacture of semiconductor devices, liquid crystal display devices, etc., and in particular concerns an exposure apparatus provided with a levelling device for matching the surface of the photosensitive substrate with the image formation plane of the projection optical system.
The present invention also concerns a stage apparatus, more specifically, a stage apparatus which is provided with a No. 1 stage which is able to move in a specified direction along a guidance plane over an antivibration stage which is held horizontally via antivibration pads, and a No. 2 stage which is mounted on this No. 1 stage and can be tilt-driven. The stage apparatus of the present invention can be used effectively as a stage for the positioning of photosensitive substrates in exposure devices, etc.
2. Discussion of the Related Art
In the past, in the manufacture of semiconductor devices, liquid crystal display elements, etc., using photolithographic techniques, an exposure apparatus has been used in which a pattern formed on a photomask (hereinafter referred to as mask) or reticle is projected and exposed on each shot area of a photosensitive substrate such as a semiconductor wafer or glass plate, etc., which has been coated with a photosensitive agent such as photoresist via a projection optical system. As an exposure apparatus, a so-called step-and-repeat type exposure apparatus, wherein the photosensitive substrate is mounted on a substrate stage which is moveable in two dimensions, and the operation of exposing the pattern image of the mask on each shot area of the photosensitive substrate is repeated by stepping the photosensitive substrate using this substrate stage, and, in particular, reductive projection type exposure apparatuses have often been used. Also, step-and-scan type exposure apparatuses have been used in which pattern exposure is performed on each shot area of the photosensitive substrate by reductive projection and, by means of a scanning exposure system, movement is performed between the shot areas in a stepping mode.
In general, since a projection optical system which has a large numerical aperture and a shallow focal depth is used in the exposure apparatus, in order to transcribe a fine pattern with high resolution, levelling control, whereby the angle of inclination of the photosensitive substrate surface is matched so as to be parallel with the angle of inclination of the image formation plane of the projection optical system, and autofocus control, whereby the height (focal point position) of the surface of the photosensitive substrate is matched with the position of the image formation plane of the projection optical system are necessary.
In order to perform levelling control, it is necessary to measure accurately the average inclination amount of local parts of or the entire photosensitive substrate surface. In the past, various such measurement methods have been proposed, for example, in Japanese Examined Patent No. [Kokoku] Hei 3-5652, Tokko Hei 4-42601, U.S. Pat. Nos. 4,084,903, 4,383,757, etc. For example, the height position in the optical axis direction (Z direction) is measured on at least 3 points on the photosensitive substrate using a gap sensor such as an air micrometer, an approximate plane formula of the photosensitive substrate surface is specified based on the measurement values thereof, and a levelling mechanism provided on the substrate stage is driven so that the approximate plane matches the image formation plane of the projection optical system.
Also, in the past, in shot areas existing on the peripheral area of the photosensitive substrate, which are shot areas for which autofocus control is difficult due to the scattering of the focal point position detection light, etc., exposure is performed in the focal point position of the shot area which is adjacent to this shot.
The sensor which measures the height position of the photosensitive substrate in the Z direction is fixed on the apparatus main body and is unable to move. Accordingly, in order to measure the Z direction positions of several points on the photosensitive substrate surface, the photosensitive substrate is moved by means of the substrate stage, and the multiple points on the photosensitive substrate are taken to the measurement point of the sensor in sequence. For this reason, when the running of the substrate stage itself carries a displacement amount in the Z direction, the Z direction displacement of the photosensitive substrate surface caused by the running of the substrate stage and the Z direction displacement within the plane of the photosensitive substrate cannot be separated, so that even if the surface of the photosensitive substrate itself is perpendicular to the Z direction, it may be judged that the photosensitive substrate surface is inclined, creating the problem that the levelling operation will be performed in error.
Problems in conventional levelling control are explained referring to FIG. 13. Here, the action of performing levelling control based on sensor measurement values having measurement points in the positions indicated by the broken line are explained making the running direction of the substrate stage the X direction and the direction parallel to the optical axis the Z direction. FIGS. 13(a) through (c) consists of diagrams explaining the concept of levelling control in the case where there is no displacement of the substrate stage running in the Z direction and FIGS. 13(d) through (f) consists of diagrams explaining the concept of levelling control when the running of the substrate stage has displacement in the Z direction.
Assuming that the surface SF.sub.1 of the photosensitive substrate 80 is inclined as shown in FIG. 13(a). First, the photosensitive substrate is positioned in the position indicated by the solid line by means of the movement of the substrate stage (85) and the height position of point P.sub.1 of the photosensitive substrate surface SF.sub.1 is measured. The X coordinate of point P.sub.1 is X.sub.1, and the height measurement position at this time is made Z.sub.1. Next, the photosensitive substrate (80) is moved to a different position on an imaginary line as indicated by the arrow by the movement of the substrate stage and the height position of another point P.sub.2 on the photosensitive substrate surface SF.sub.1 is measured. The X coordinate of point P.sub.2 is made X.sub.2, and the height measurement value is made Z.sub.2.
From the coordinate values (X.sub.1, Z.sub.1) of point P.sub.1 and the coordinate values (X.sub.2, Z.sub.2) of point P.sub.2 at this time, the exposure apparatus recognizes that the surface SF.sub.1 of the photosensitive substrate is inclined as shown in FIG. 13(b). Accordingly, as shown in FIG. 13(c), levelling control is performed so that the mounting object table 81 upon which the photosensitive substrate 80 is mounted is inclined by operating the levelling mechanisms 82a, 82b of the substrate stage, and the surface SF.sub.1 of the photosensitive substrate 80 becomes horizontal. In this way, if the running of the substrate stage 85 becomes displaced in the Z direction, a conventional exposure apparatus can perform suitable levelling control based on the height measurement values.
On the other hand, when, as indicated by the wavy imaginary line in FIG. 13(d), the running of the substrate stage 85 has displacement in the Z direction, a conventional exposure apparatus cannot perform levelling control. It is assumed, as shown in FIG. 13(d), that the photosensitive substrate 87 has no inclination within the plane. Initially, the photosensitive substrate 87 will be positioned as indicated by the solid line by the movement of the substrate stage 85, and the height position of point P.sub.3 of the photosensitive substrate surface SF.sub.2 is measured. Here it is assumed that the X coordinate of point P.sub.3 is X.sub.3, and the height measurement value at this time is Z.sub.3. Next, the photosensitive substrate 87 is moved by the movement of the substrate stage up to a position indicated by the broken line as shown by the arrows, and the height of another point P.sub.4 on the photosensitive substrate surface SF.sub.2 is measured. At this time, since the running of the substrate stage 85 has displacement in the Z direction, the photosensitive substrate 87 is moved in the Z direction as well, and the measurement value of the height of point P.sub.4 is assumed to become Z.sub.4. The X coordinate of point P.sub.4 is X.sub.4.
At this time, from the coordinate values (X.sub.3, Z.sub.3) of point P.sub.3 and the coordinate values (X.sub.4, Z.sub.4) of point P.sub.4, the exposure apparatus recognizes that the surface SF.sub.2 of the photosensitive substrate is inclined as indicated in FIG. 13(e), despite the fact that it is actually horizontal. Accordingly, control is performed so that the levelling mechanism 82a, 82b of the substrate stage 85 are operated, the mounting object table 81 upon which the photosensitive substrate 87 is mounted is tilted, and the height position Z.sub.3 of point P.sub.3 and the height position Z.sub.4 of point P.sub.4 are made equal. As a result, as shown in FIG. 13d, faulty levelling control is performed, and the surface SF.sub.2 of the photosensitive substrate 87 ceases to be horizontal.
Also, in conventional exposure apparatuses, in shots in the peripheral area of the photosensitive substrate, when exposure is performed in the focal point position of the adjacent shot without detecting the focal point position in the exposure position, even if there is change in the Z direction due to the running of the substrate stage, there is a problem that error due to displacement of the focal point position will result because focal point position correction has not been performed.
In the past, in the manufacture of semiconductor elements or liquid crystal display elements, etc., by photolithographic processes, an exposure apparatus has been used wherein the image of a pattern formed on a mask or reticle is transferred via a projection optical system onto an exposure target substrate such as a wafer or glass plate. In this type of exposure apparatus, a stage apparatus is used wherein a sample stage in which movement of 3 axes, movement in the up-down direction (Z), rotation around the X axis, and rotation around the Y axis, or on 4 axes, adding rotation on a Z axis is mounted on an XY stage which is able to move within a 2-dimensional plane in perpendicular biaxial directions (normally the XY biaxial directions). In this case, the sample stand as a result can have positional and attitude control of 5 degrees of freedom or 6 degrees of freedom, and the position of the sample stand in the XY 2-dimensional direction is measured with high accuracy by means of a lightwave interferometer, generally a laser interferometer, via a reflecting mirror (moving mirror) fixed on the sample stand. Furthermore, a light source, reticle stage, projection optical system, reflecting mirror (fixed mirror) which forms the light generating part and standard of the laser interferometer, a focus detection system, which measures positional displacement of the focal planes of the exposure target substrate and projection optical system in the optical axis direction, and a leveling detection system, which measures the inclination of the exposure target substrate and focal plane (image formation plane), etc., are mounted on a stand to which the stage base is rigidly connected.
At the time of exposure, the XY stage is moved 2-dimensionally in the XY plane, the exposure position (shot region) of the exposure target substrate is positioned in the pattern projection position of the projection optical system, and next, or at the same time as the XY movement, the sample stand is Z-driven based upon the measurement results of the focus detection system so as to enter the region of the focal depth of the projection optical system, simultaneously the inclination of the sample stand is adjusted based upon the measurement to results of the leveling detection system so that the exposure target substrate and image formation plane will be parallel, and when all deviations have entered allowable levels, exposure is performed.
When the inclination of the exposure target substrate surface and image formation plane are matched, the sample stand is tilted, but since the moving mirror is also tilted together with the sample stand at this time, the angle formed by the laser beam optical axis from the interferometer and the moving mirror reflecting face changes. Specifically, the laser beam is no longer perpendicularly incident to the moving mirror reflecting face, and as a result error is produced in the XY coordinates of the sample stand as measured by the laser interferometer.
The principal error is generally referred to as Abbe error and cosine error, and when the difference in height between the interferometer beam and the exposure target substrate surface is "h" and the distance in a specified measurement direction, for example, the X direction, between the moving mirror reflecting face and the exposure position is "S," and the amount of change in the inclination in the Y axis of the sample stand with regard to the interferometer laser optical axis is ".alpha.," the X direction error Err can be represented as EQU Err=Abbe error+cosine error=h.times..alpha.+S.times.(1-cos.alpha.).
In the past, the error has been obtained by means of calculation assuming the inclination .theta. of the sample stand that has been detected by the measurement device mounted on the XY stage as being the same as the .alpha., and error has been eliminated by correcting the position of the XY stage or the position of the reticle.
Nevertheless, when the XY stage is moved in the X direction or Y direction, depending upon errors in flatness, etc., in the guidance plane, rotation around the X axis or the Y axis can occur in the XY stage, and since the inclinations .theta. and .alpha. cannot be said to match in a strict sense, as the positioning precision of the exposure target substrate becomes more and more strict, the position measurement error of the laser interferometer caused by this difference between .theta. and .alpha. has come to be a problem.
Moreover, in precision equipment such as normal exposure apparatuses, etc., because of the necessity for insulation of the effects of vibration from the setting floor on a microgram scale, the fixed base upon which the XY stage and its stage base are mounted is held horizontally by means of antivibration pads, so that there is some inclination of the fixed base with regard to an absolute standard due to the movement of the center of gravity accompanying movement of the XY stage, in such cases, the necessity arises to position the XY stage taking into consideration the effects of this inclination as well.